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Hot-air balloons float because the air inside the balloon is less dense than the outside air.
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Energy Density

A tornado is the most destructive natural storm. You might think that
this also means that tornadoes are the strongest storms; that's not the
case. In fact, a thunderstorm which produces a tornado can have 40,000
times more energy than a tornado! Then why are tornadoes so much more
destructive than thunderstorms?
Tornadoes have a greater energy density than
thunderstorms. They don't have as much energy but the energy they do
have is packed into smaller spaces. Another way of thinking about this
is with rocks and feathers. A bag of feathers might outweigh a rock, but
put them both in water and the feathers will float while the rock sinks
because the feathers are less dense. Tornadoes are so destructive
because they strike a very small area.

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